Grand nieces

[Kit]

I ordered some wills for my Christmas present and received a few back yesterday. Looking at the will of what I thought was my 4g grandmother has me confused.

She leaves money to 4 grandsons from her son John, who fit in my tree but leaves money to my 2g grandmother and her sister but calls them grandnieces, not granddaughters, which I think they should be.

This was in 1881, did they use the terms interchangeably back then or have I made a mistake in my tree?

I'm not putting up names yet as there is other new information I want to follow up from the will as well which might or might not help with some things.